So-called Thin Provisioning is known as a technique to achieve a reduction of TCO (Total Cost of Ownership). In Thin Provisioning, real storage resources expected to be used in the future are not introduced beforehand, unlike the conventional storage systems. Specifically, storage resources supplied by a physical drive such as a hard disk drive are managed as a storage pool; virtual volumes configured by using real storage resources of storage pools are provided to a server apparatus (an external device); and when real storage resources become in short supply, a necessary amount of real storage resources is supplied to the storage pools as supplementary resources. According to Thin Provisioning, various advantages may be obtained such as facilitated capacity design of the storage system, reduction of initial introduction costs, reduction of operational costs such as electric power and air conditioning costs.
As a method of controlling storage resources virtually, for example, Patent Literature (PTL) 1 describes a configuration of a storage control system. In the storage control system, upon receipt of a read or write request from a higher level apparatus which is aware of a virtual storage unit, a virtual storage area in the virtual storage unit is associated with a logical storage area in a logical storage device, and data are exchanged between the logical storage area and the higher level apparatus via the virtual storage areas.